This invention relates generally to sensing virtual ground flash memory arrays.
In virtual ground flash memory arrays, sneak currents may occur during sensing. One way to reduce sneak currents is to provide a so-called input/output (I/O) break. The I/O break may be a column of programmed cells. This column of programmed cells is positioned between two adjacent input/output groups. Each input/output group may be coupled to a different sense amplifier so that it is possible to sense cells within different groups at the same time.
A problem with the programmed cell I/O break occurs with erase verify. In erase verify it is desirable to verify, after erasing a block in the array, that the block was actually erased. To do so, the cells are read after the erase to verify that they are in the right state. However, when the block is erased, the cells in the I/O break are also erased and, therefore, they can not act as I/O break any more. The array left in this state will cause sneak currents during the erase verify cycle.
Thus, there is a need for ways to reduce sneak currents, especially during the erase verify cycle.